Thermodynamic and quantum-chemical study of the oxidative dehydrogenation of ethane to ethylene

Abstract

A major amount of ethylene in the industry is cur rently produced by the pyrolysis of hydrocarbon feed stock (ethane, ethane-propane-butane mixture, or straight run gasoline fraction) in a tubular furnace. The yield of olefins (ethylene + propylene) is 60-66%. The development of the process is focused on improving the existing technology. However, despite the progress associated with changes in the arrange ment of the radiant coil pipes in the furnace, the designing of effective transfer line exchangers, and the introduction of furnaces with a short residence time of feedstock in the reaction zone, the potentialities of this process are limited, especially in the case of feed stock prone to enhanced coking [1]. The necessity to expand the resource base, in particular, involvement of the components of natural, associated, and refinery gases in processing requires searching for fundamen tally new methods of implementation of the process.Thus, since the middle of the last century, intensive studies are conducted on the development of processes for catalytic dehydrogenation of lower alkanes to the corresponding olefins. Use of a catalyst makes it pos sible to increase the feedstock conversion as compared with the conventional pyrolysis process and improve the process selectivity. However, from the viewpoint of practical application, this dehydrogenation process also has drawbacks associated in particular with intense coking and the need to conduct oxidative regeneration.These drawbacks are eliminated by using an oxi dant in the process. The use of an oxidant in the dehy drogenation of lower alkanes has a number of potential benefits: it improves the performance of the pyrolysis process, allows bypassing the restrictions imposed by thermodynamics on the product composition and conducting the process at lower temperatures due to the exothermic oxidation reactions directly in the reaction zone, and increases the catalyst on stream time owing to possible coke burn up during the reac tion [2,3].In view that this line of research holds enough promise, we performed comparative thermodynamic calculation of the equilibrium product composition for thermal and oxidative dehydrogenations of ethane and quantum chemical calculation of the activation energy of ethane dehydrogenation in the active metal phase of the catalyst molybdenum oxide МоО 2 .The equilibrium concentrations of the reaction components were calculated in the ideal gas approxi mation [4, 5]. Table 1 shows values for the thermody namic functions enthalpy ΔH, entropy ΔS, and Gibbs free energy ΔG of the two simple reactions:These reactions are interesting in that hydrogen and water are produced in reactions (1) and (2), respectively. Naturally, the second reaction is preferred from the standpoint of obtaining pure ethylene.As can be seen from Table 1, these reactions signif icantly differ in thermodynamic characteristics. Enthalpy ΔH slightly depends on temperature, reac tion (1) is strongly endothermic, and reaction of (2) is exothermic. Gibbs energies ΔG of the rea...

A pseudo-local heat transfer approach in a low tube to particle diameter ratio packed bed catalytic reactor: Oxidative dehydrogenation of ethane as a case study

“…Research efforts, aiming at improving the performance of the wall-cooled packed bed reactor with low dt/dp, have been focused on developing pseudo-continuous models to design [1,8,[15][16][17][18][19][20][21], optimize [22][23][24][25][26][27] or simply understand the complex interaction between transport phenomena and reaction kinetics in wall-cooled packed bed reactors. Because of its high sensitivity to the operating conditions [1,13,14], a diversity of one [28][29][30] and two [1,5,8,9,12,13,15,21,[31][32][33] dimensional models, such as pseudo-homogeneous models [1,5,8,9,12,13,[15][16][17][18][19][20][21]31,[33]…”

Oxygen Transfer at Metal-Reducible Oxide Nanocatalyst Interfaces: Contrasting Carbon Growth from Ethane and Ethylene

“…The thermal dehydrogenation of ethylene to acetylene (C 2 H 4 → C 2 H 2 + H 2 ) is an endothermic reaction (Δ H = 174 kJ/mol). However, once C 2 H 2 is formed, subsequent decomposition reactions will occur rapidly to form carbon and hydrogen. ,− Ethane’s thermal dehydrogenation to ethylene (C 2 H 6 → C 2 H 4 + H 2 ) is also an endothermic reaction (Δ H = 136 kJ/mol). , However, an alternative way to dehydrogenate C 2 H 6 is through partial oxidation, otherwise known as oxidative dehydrogenation (ODH) (C 2 H 6 + 1/2 O 2 → C 2 H 4 + H 2 O), which is exothermic (Δ H = −106 kJ/mol) . Consequently, the dehydrogenation of C 2 H 6 is thermodynamically favored in the presence of an oxidizing agent.…”

Unravelling the redox mechanism and kinetics of a highly active and selective Ni-based material for the oxidative dehydrogenation of ethane

“…On the other hand, in the MvK-based mechanism, the adsorption of the compounds is neglected, and ethane and ethylene, thus, react on the oxidized active site directly from the gas phase, reducing them in the process and explaining the replenishment step discussed above. Based on the thermodynamics of ODH-C 2 , 73 the hydrocarbon oxidation reactions are considered irreversible. All the mechanisms in Table 2 incorporate the corresponding Horiuti number, σ j , that is used to describe the number of times that every reaction step must occur to complete a catalytic reaction cycle according to the general reaction network.…”